1. Field of the Invention
The present invention relates to method and apparatus for controlling a reproducing/recording speed of an optical disk in an optical disk device.
2. Description of the Related Art
FIG. 1 is a schematic block diagram of a general optical disk player, which comprises an optical pickup unit 11 for detecting recorded signals from an optical disk 10 inserted; a driver 21 for driving a sled motor 12a to move the optical pickup 11 and a spindle motor 12b to rotate the optical disk 10; an R/F unit 20 for equalizing and shaping the RF signal reproduced by the pickup 11 into binary signals; a servo unit 30 for controlling the optical pickup 11 and the driver 21; a digital signal processor (DSP) 30 for processing the binary signals from the R/F unit 20 into 14-bit EFM data; an EFM demodulator 50 for demodulating each 14-bit EFM data into a corresponding 8-bit data; a CIRC decoder 70 for detecting and correcting errors of the demodulated data in an ECC data block; and a controller 60 for controlling the servo unit 30 and the disk reproduction speed depending upon whether the data error is corrected or not.
The detailed reproduction operation of the optical disk player structured as above is as follows. First, the optical disk 10 is inserted and then starts to rotate. The recorded signals are reproduced as high frequency (referred as xe2x80x9cRFxe2x80x9d hereinafter) signals by the optical pickup 11. The reproduced RF signals are equalized and then converted into binary signals by the R/F unit 11.
Meanwhile, the controller 60 distinguishes the type of the inserted optical disk 10 based on the reproduced RF signals. For this type distinction, the controller 60 compares the reproduced signal level with the pre-determined standard level, and discriminates the type of the optical disk 10 according to the comparison result.
With regard to the comparison result, if the RF signal level is below the standard level, the controller 60 considers the optical disk 10 to be a writable one, for example CD-R or CD-RW, and if it is above the standard level, the controller 60 considers the disk 10 to be a read-only disk such as CD-ROM.
After the type of disk decision has been made, the controller 60 rotates the optical disk 10 at a reproduction speed according to the determined disk type. That is, the controller 60 applies a driving voltage corresponding to its maximum speed to the spindle motor 12b through the servo unit 30 and the driver 21 if the determined type is a read-only, and applies a driving voltage corresponding to the maximum speed divided by a predetermined value to the spindle motor 12b to rotate the optical disk 10 at a lower speed.
Under the condition that the disk 10 is being rotated at the chosen speed, the RF signals reproduced from the rotating optical disk 10 by the pickup 11 are converted into binary signals in the R/F unit 20 as explained above. The binary signals are restored into EFM modulated digital data by the DSP 30.
When the DSP 30 detects one or more data errors which may be caused from signal drop out etc. during the data restoring process, it generates an error-notifying signal and sends it to the controller 60. The EFM demodulator demodulates series of the restored 14-bit digital data into series of corresponding 8-bit data on the basis of the pre-stored EFM conversion table.
Meanwhile, when the specific signal indicating that the reproduction error is received from the DSP 30, the controller 60 controls the CIRC decoder 70 to try to correct the error of the demodulated digital data received from the EFM demodulator, so that the CIRC decoder 70 tries to recover the error data into normal data a preset number of times.
However, if the error data is not recovered to a normal data (even though the error correction process has been performed several times), the controller 60 controls the driving voltage applied to the spindle motor 12b through the servo unit 30 and the driver 21 to adjust the rotation speed of the optical disk 10 to a lower speed, re-detects the recorded signals of disk location where the error data is reproduced through the optical pickup 11, and then performs the above-explained error correction process again.
In the conventional reproduction method for an optical disk described hereinbefore, the reproduction speed of an optical disk is changed to a lower speed and then the corresponding data area is re-read if an error data, which may be caused from an abnormal disk condition, reproduced from an optical disk cannot be recovered to normal data even after error correction trials of the preset number. However, such retrials to correct error and data re-reading at a reduced speed causes delay time in reproduction, which results in discontinuity in video or audio being reproduced.
In addition, in the conventional optical disk player, the gain values of a servo unit for tracking and focussing servo control are selected from among only two values (appropriate for high and low speed), so that the tracking and focussing control of an optical pickup during the gradual speed adjustment cannot be performed accurately.
It is an object of the present invention to provide method and apparatus for controlling a disk speed in advance according to a distinguished disk condition to reduce delay time in reproduction while maintaining precise servo control.
In order to achieve the objective, another method according to the present invention comprises the steps of detecting a disk type or a disk condition based on the characteristics of a reproduced signal from an optical disk; displaying possible reproduction speeds on a screen according to the detected disk type or disk condition; and executing a servo control program appropriate for the reproduction speed selected from among the displayed reproduction speeds.